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941.
Within the framework of a simple electrostatic model, as compared to recent experimental results, we here discuss the stability
of very weakly bound molecular negative ions. In contrast with the case of conventional valence anions, the excess electron
is then located in a very diffuse orbital and is mainly bound by electrostatic dipolar, quadrupolar, and polarization forces,
at large distances from the neutral molecular core. By fitting a single repulsion parameter of the model to the available
experimental data, it is possible to make quantitative predictions of the excess-electron binding energies in these species.
Critical values of the dipole moment, quadrupole moment or polarizability required for the observation of stable multipole-bound
negative ions are predicted and compared to available experimental data and ab initio calculations.
Received October 24, 2001; accepted for publication November 16, 2001 相似文献
942.
In this paper we deal with the numerical solution of movingboundary problems of two-phase Stefan type. Based on an implicitdiscretization in time and the use of continuous, piecewiselinear finite elements in the space variables with respect tothe weak formulation of the problem, a globally convergent multi-gridalgorithm is developed. That algorithm strongly relies on thevariational characterization of the fully discretized problemas the unconstrained minimization of a subdifferentiable convexobjective functional. Numerical results indicate a significantimprovement in efficiency compared with previous multi-gridapproaches. 相似文献
943.
A broad range echelle spectrograph with a CCD matrix detector is developed for different applications in atomic spectroscopy. The compact optical design in combination with a dispersive entrance slit illumination offers a low stray light level and high throughput in the UV spectral region comparable only with spectrographs of higher focal length. Ray tracing calculations for typical wavelengths and the multi-line spectrum of an iron arc show the excellent overall spectrum quality. The subtraction of two partial spectra of different steel alloys demonstrates the spectra evaluation possibilities of the CCD spectrograph. 相似文献
944.
Summary Observation of fluorescence reactions on TLC plates is a valuable additional tool within the scope of screening procedures for many toxicologically relevant substances commonly encountered in clinical- and forensic-toxicological analysis. The reactions are based on native fluorescence without any treatment and on reactions obtained with an approved derivatization procedure. Due to the enormous sensitivity of the fluorescence detection, the method is also applicable to very low concentrations and small amounts of biological materials. The procedures described in this article have proven their high pragmatic usefulness in many practical cases.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
945.
G. Baldsiefen H. Hübel W. Korten U. J. van Severen J. A. Cizewski N. H. Medina D. R. Napoli C. Rossi Alvarez G. Lo Bianco S. Signorelli 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):337-338
High-spin states in196Pb have been populated using the reaction170Er(30Si,4n). The previously observed shears bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin. 相似文献
946.
J. Urban H. Sack-Kongehl K. Weiss 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(1):73-83
Structure and reactivity with oxigen of Cu clusters in the size range of 4.5±2.5 nm created by the inert gas aggregation technique were studied by HREM. The pure Cu clusters investigated under clean conditions show the structures of MTP's with a small lattice dilatation of the (111) plane of 1.25%. For icosahedral and decahedral particles this dilatation corresponds to a splitting of the nearest neighbour distance showing two different values, i.e. dilatation of 2.2% and contraction of 2.8% for the two edges of the deformed tetrahedral subunits, respectively. Oxidation at room temperature and air pressure of 1 bar only begins after a few minutes of exposure to air, after having undergone creation of probably non-stoichiometric intermediate states in the cuprite Cu2O structure with the bulk values of the bond lengths. 相似文献
947.
The temperature dependence of the NMR chemical shift of129Xe dissolved in liquid alkanes is examined in the context of the reaction field model. An essential feature of the theory is the inclusion of the temperature dependence of the density of thesolvent. The theory of free volume for liquids is incorporated into the reaction field model to account for this temperature dependence. Comparison of the theory with previously reported measurements indicates the sensitivity of the129Xe chemical shift to the free volume of liquids. Incorporation of free volume improves the agreement between measurement and theory for branched alkane solvents, and resolves the origin of the 62 ppm intercept in the plot of reaction field as a function of129Xe chemical shift for the n-alkanes. 相似文献
948.
C. B?uerle Yu M. Bunkov S. N. Fisher H. Godfrin G. R. Pickett 《Czechoslovak Journal of Physics》1996,46(Z1):5-6
During studies of the impact of single neutrons on superfluid3He at around 100μK we have measured the thermal energy released in the superfluid following the nuclear reaction, n+3He→p+3H+764keV. However, we find that the measured energy deposited in the quasiparticle system shortly after this reaction is substantially
less than what we expect. We believe that this energy deficit represents that energy which has gone into the creation of vortices,
in analogy to the creation of cosmic strings in the early universe via the Kibble mechanism. Furthermore, from the magnitude
of the deficit, we can infer the vortex density which compares favorably with that predicted in Zurek’s scenairo. 相似文献
949.
950.